Ethical Stem Cell Research Tax Credit Act of 2008 - Amends the Internal Revenue Code to allow a tax credit for 30% of qualified stem cell research expenses paid or incurred in a taxable year. Defines "qualified stem cell research expenses" as expenses for carrying out basic and applied research to develop techniques for the isolation, derivation, production, testing, and human clinical use of stem cells that may result in improved understanding of or treatments for diseases and other adverse health conditions. Prohibits a tax credit for any research expenses that may involve: (1) the creation of a human embryo for research purposes; (2) the destruction of or discarding of, or risk of injury to, a human embryo; or (3) the use of any stem cell for prohibited purposes.